Oppenheimer Wolff & Donnelly | 731 followers on LinkedIn. Oppenheimer is a 129-year old, Minneapolis-based law firm. It’s a recognized leader in providing practical legal counsel to businesses of all sizes—from start-ups to Fortune 500 corporations. The firm’s core practices include corporate finance, mergers and acquisitions, securities, real estate finance, lending and business litigation, with specialty practices in complex healthcare litigation, employee benefits, intellectual property and labor and employment.